The electronic device fabrication industry requires various liquid chemicals as raw materials or precursors to fabricate integrated circuits and other electronic devices. This need arises from the requirement to dope semiconductors with various chemicals to provide the appropriate electrical properties in the semiconductor for transistors and gate oxides, as well as circuits requiring various metals, barrier layers, vias. Additionally, dielectric layers are needed for capacitors and interlayer dielectric requirements. Fabrication requiring subtractive technologies require resists, planarization chemistries and etchants.
All of the chemicals that are used in these applications are required in high purity conditions to meet the stringent requirements of the electronic fabrication industry imposed by the extremely fine line width and high device densities in current and future electronic devices being fabricated with those chemicals.
A part of the effort to provide high purity chemicals is the design and structure of the containers and systems which delivery such chemicals to the reactor or furnaces where the electronic devices are being fabricated. The purity of the chemicals can be no better than the containers in which they are stored and the systems through which they are dispensed.
In addition, it is important to monitor the quantity of high purity chemical available during its use in the electronic device fabrication process. Electronic devices are fabricated in quantities of several hundred at a time per semiconductor wafer, with the size of individual wafers being processed expected to be larger in future fabrication processes. This makes the value of the yield of electronic devices being processed on wafers very high, resulting in considerable cost if processing or fabrication occurs when the high purity chemical is unavailable inadvertently. Thus, the electronic fabrication industry has used monitoring of high purity chemical quantity a part of their scheme in their fabrication processes.
Not infrequently, the high purity chemicals used in the electronic device fabrication process also are very expensive due to their exotic or complex makeup, the low volumes need in fabrication (i.e., dopants are needed in only low levels) and the requirement for very tight product specifications (i.e., high purity and the absence of a wide array of contaminants particularly metals). As a result of the high expense of these high purity chemicals, it is desired to consume as much of the chemical as possible with out running dry. Thus residual chemical in chemical containers, i.e., heals, is desired to be minimized, but complete consumption is also not desired because in automated fabrication processing, such as electronic device fabrication, operating to a run dry condition can result in wafer defects or reduction in yields, which are unacceptable to industry and also very costly.
To address the issues of purity and monitoring of chemical quantity available for use, the industry has made various attempts to achieve those goals.
U.S. Pat. No. 5,199,603 discloses a container for organometallic compounds used in deposition systems wherein the container has inlet and outlet valves and a diptube for liquid chemical dispensing through the outlet. However, no level sensor is provided.
U.S. Pat. No. 5,562,132 describes a container for high purity chemicals with diptube outlet and internal float level sensor. The diptube is connected to the integral outlet valve. However, internal float level sensors are known particle generators for the high purity chemicals contained in the container.
U.S. Pat. No. 4,440,319 shows a container for beverages in which a diptube allows liquid dispensing based upon a pressurizing gas. The diptube may reside in a well to allow complete dispensing of the beverage. Level sense is not.
U.S. Pat. No. 5,663,503 describes an ultrasonic sensor, which is known to be used to detect liquid presence in a vessel. Invasive and non-invasive sensors are described.
U.S. Pat. No. 6,077,356 shows a reagent supply vessel for chemical vapor deposition, which vessel has a sump cavity in which the liquid discharge dip tube terminates, as well as a liquid level sensor terminates. Ultrasonic sensors are contemplated (col. 6, line 37), but in that embodiment, the patent expressly teaches that the sensor does not utilize the sump for sensing operations (col. 6, line 38–43). Good chemical utilization occurs only when the vessel is in the full upright position.
U.S. Pat. No. 4,531,656 shows a container with a rounded floor and a diptube 81.
U.S. Pat. No. 5,069,243 shows a sewage tank with a suction pipe 5 and a level sensing device 8.
U.S. Pat. No. 5,782,381 shows a container for herbicides with a discharge tube 19 and a sight tube 13.
The shortcomings of the prior art in addressing the goals of purity and efficient chemical utilization are overcome by the present invention, which provides high purity containment, no chemical entrapment areas (i.e. sump, sidewall to bottom and top transition points) to harbor residual chemical during the container empty clean and refill procedure, a symmetrical design feature enabling cost effective manufacturing and polishing to the mirror finishes (10Ra) required for high purity chemical containers to maintain chemical purity, at the low and empty level sense points where the level precision is most important the smaller cross sectional area of the container concave section enables a more precise measurement of liquid and avoidance of contamination or particle generation during level sensing, and efficient chemical utilization approaching complete chemical utilization without reaching chemical run dry conditions. Other advantages of the present invention are also detailed below.